低渗透多孔介质变渗透率数值模拟方法

根据流体在低渗透多孔介质中的渗流特征,建立了低渗透多孔介质数学模型,通过引入无因次渗透率变化系数描述低速非达西渗流规律,并基于黑油模型数值模拟系统,开发了低渗透多孔介质变渗透率数值模拟软件。采用矿场实际数据,分别使用达西渗流、考虑启动压力梯度为常数的拟线性渗流和变渗透率渗流模型,对五点井网进行模拟计算,对比分析了不同渗流规律下的油井产油量、含水率、含油饱和度及不同时间的地层渗透率分布。结果表明,变渗透率渗流模型计算的油井产油量、含水率和含油饱和度分布介于达西渗流和拟启动压力梯度渗流模拟结果之间,油水井附近地层渗流能力强,远离主流线地层渗流能力弱;井距越小,地层渗流能力越强;流体在低渗透多孔介质的渗流过程中,达西渗流仅发生在井筒附近小面积区域内,地层大部分区域发生变渗透率渗流,且占据了地层渗流的主导地位,变渗透率数值模拟方法弥补了其他方法未考虑渗透率变化因素的不足,变渗透率数值模拟软件能够更准确地预测流体在低渗透多孔介质中的流动特征。

Numerical Simulation of Variable Permeability of Low-permeability Porous Media

According to the fluid flow characteristics in low-permeability porous media, a mathematical model is built, and the dimensionless permeability variation coefficient is used to describe the low-velocity non-Darcy flow. The variable permeability numerical simulation software is developed based on the black-oil model. Actual field data is used to simulate a five-spot well unit. The comparative analysis of Darcy flow, quasi-linear flow which assumes the starting pressure gradient to be constant and variable permeability flow, is carried out in the simulation. The oil production, water cut, oil saturation distribution and permeability distribution are compared, which indicates that the flow ability of the formation near the oil and water well is strong while the flow ability of the formation far away from the main stream line is weak; the formation flow ability becomes stronger with the decrease of the well spacing. When the fluid flows in low-permeability porous media, Darcy flow only occurs in area near the wells, and the variable permeability flow area is much larger than that of Darcy flow. The variable permeability numerical simulation results show the limitations of quasi-linear flow, which can not describe the change of liquid permeability with pressure gradient. The variable permeability flow plays a dominant role in fluid flow and the variable permeability numerical simulation software could be used to simulate the percolating process of the fluid in the low-permeability porous media quite accurately.